imr-pinro_2-2014.pdf (3.893Mb)

J O I N

T

R E P O R T S E R I E S

I M R / P I N R O

2 2014

Fish investigations in the Barents Sea

winter 2013-2014

This report should be cited as:

Mehl, S., Aglen, A., Bogstad, B., Dingsør, G.E., Gjøsæter, H., Godiksen, J., Johannessen, E., Korsbrekke, K., Murashko, P.A., Russkikh, A.A., Staby, A., Wenneck, T. de Lange,

Wienerroither, R. 2014. Fish investigations in the Barents Sea winter 2013-2014.

IMR/PINRO Joint Report Series 2014(2), 73 pp. ISSN 1502-8828.

Fish investigations in the Barents Sea winter 2013-2014

Sigbjørn Mehl, Asgeir Aglen, Bjarte Bogstad, Gjert E. Dingsør, Harald Gjøsæter, Jane Godiksen, Edda Johannesen, Knut Korsbrekke,

Arved Staby, Thomas de Lange Wenneck and Rupert Wienerroither Institute of Marine Research

P.O. Box 1870 Nordnes, N-5817 Bergen, Norway

Pavel A. Murashko and Alexey A. Russkikh PINRO77

6 Knipovich Street, 183038 Murmansk. Russia

CONTENTS

Preface ... 6

1. Introduction ... 7

2. Methods ... 8

2.1 Acoustic measurements ... 8

2.2 Swept area measurements... 10

2.3 Sampling of catch and age-length keys. ... 13

3. Survey operation and material ... 15

4. Hydrography ... 18

5. Total echo abundance of cod and haddock ... 18

6. Distribution and abundance of cod ... 21

6.1 Acoustic estimation ... 21

6.2 Swept area estimation ... 23

6.3 Growth and survey mortalities ... 27

6.4 Stomach sampling ... 32

7. Distribution and abundance of haddock ... 40

7.1 Acoustic estimation ... 40

7.3 Growth and survey mortalities ... 46

8. Distribution and abundance of redfish ... 50

8.1 Acoustic estimation ... 50

8.2 Swept area estimation ... 50

9. Distribution and abundance of greenland halibut and long rough dab ... 55

9.1 Greenland halibut ... 55

9.2 Long rough dab ... 57

10. Distribution and abundance of capelin, polar cod and blue whiting ... 60

10.1 Capelin... 60

10.2 Polar cod ... 61

10.3 Blue whiting ... 61

11. Registrations of other species ... 63

12. SUMMARY ... 66

Cod ... 66

Haddock ... 66

Greenland halibut ... 67

Long rough dab ... 67

Capelin ... 67

Polar cod ... 67

Blue whiting ... 67

13. REFERENCES ... 68

Appendix 1. Annual survey reports 1981-2014 ... 70

Appendix 2. Changes in survey design, methods, gear etc. ... 72

Appendix 3. Scientific participants 2013 – 2014 ... 73

Preface

Annual catch quotas and other regulations of the Barents Sea fisheries are set through negotiations between Norway and Russia. Assessment of the state of the stocks and quota advices are given by the International Council for the Exploration of the Sea (ICES). Their work is based on survey results and international landings statistics. The results from the demersal fish winter surveys in the Barents Sea are an important source of information for the annual stock assessment.

The development of the survey started in the early 1970s and focused on acoustic measurements of cod and haddock. Since 1981 it has been designed to produce both acoustic and swept area estimates of fish abundance. Some development has taken place since then, both in area coverage and in methodology. The development is described in detail by Jakobsen et al. (1997), Johannesen et al. (2009) and Appendix 2. At present the survey provides the main data input for a number of projects at the Institute of Marine Research, Bergen:

- monitoring abundance of the Barents Sea demersal fish stocks - mapping fish distribution in relation to climate and prey abundance - monitoring food consumption and growth

- estimating predation mortality caused by cod

This report presents the main results from the surveys in January-March 2013-2014. The

surveys were performed with the Norwegian research vessels “Johan Hjort” and “Helmer

Hanssen” and the Russian research vessels “Fridtjof Nansen” and “Vilnyus”. Annual survey

reports since 1981 are listed in Appendix 1, and names of scientific participants are given in

Appendix 3.

1 Introduction

The Institute of Marine Research (IMR), Bergen, has performed acoustic measurements of demersal fish in the Barents Sea since 1976. Since 1981 a bottom trawl survey has been combined with the acoustic survey. Typical effort of the combined survey has been 10-14 vessel-weeks, and about 350 bottom trawl hauls have been made each year. Most years three vessels have participated from about 1 February to 15 March.

The purpose of the investigations is:

x Obtain acoustic abundance indices by length and age for cod, haddock and redfish

x Obtain swept area abundance indices by length (and age) for cod, haddock, redfish and Greenland halibut

x Map the geographical distribution of those fish stocks x Estimate length, weight and maturity at age for those stocks

x Collect and analyse stomach samples from cod, for estimating predation by cod x Map the distribution of maturing/prespawning capelin

Data and results from the survey are used both in the ICES stock assessments and by several research projects at IMR and PINRO.

From 1981 to 1992 the survey area was fixed (strata 1-12, main areas ABCD in Fig. 2.1). Due

to warmer climate and increasing stock size in the early 1990s, the cod distribution area

increased. Consequently, in 1993 the survey area was extended to the north and east (strata 1-

23, main areas D’ES in Fig. 2.1) in order to obtain a more complete coverage of the younger

age groups of cod, and since then the survey has aimed at covering the whole cod distribution

area in open water. For the same reason the survey area was extended further northwards in

the western part in 2014 (strata 24-26 in Fig. 2.1). In most years since 1997 Norwegian

research vessels have had limited access to the Russian EEZ, and in 1997, 1998 and 2007 the

vessels were not allowed to work in the Russian EEZ. In 1999 the coverage was partly

limited by a rather unusually wide ice-extension. Since 2001, except in 2006 and 2007,

Russian research vessels have participated in the survey and the coverage has been better, but

for various reasons not complete in most years. In 2008-2014 Norwegian vessels had access

to major parts of the Russian EEZ. The coverage was more complete in these years, especially

in 2008, 2011 and 2014. In 2009, 2010, 2012 and 2013 the coverage in eastern areas was

more limited due to strict rules regarding handling of the catch, bad weather or vessel

problems. Table 3.6 summarizes degree of coverage and main reasons for incomplete

coverage in the Barents Sea winter 1981-2014.

2 Methods

2.1 Acoustic measurements

The method is explained by Dalen and Smedstad (1979, 1983), Dalen and Nakken (1983), MacLennan and Simmonds (1991) and Jakobsen et al. (1997). The acoustic equipment has been continuously improved. Since the early 1990s Simrad EK500 echo sounder and Bergen Echo Integrator (BEI, Knudsen 1990) have been used. The Simrad ER60 echo sounder and the Large Scale Survey System (LSSS, Korneliussen et al. 2006) has replaced the EK500 and BEI; on R/V “Johan Hjort” since the 2005 survey and on R/V “Helmer Hanssen” since the 2008 survey. On the Russian vessels EK 500 was used from 2000 to 2004 and ER60 since 2005.

In the mid 1990s the echo sounder transducers were moved from the hull to a retractable centreboard, on R/V “Johan Hjort” since the 1994 survey and on R/V “Jan Mayen” since the 2008 survey. This latter change has largely reduced the signal loss due to air bubbles in the close to surface layer. None of the Russian vessels have retractable centreboards.

On the Norwegian vessels acoustic backscattering values (s

) are stored at high resolution in LSSS. After scrutinizing and allocating the values to species or species groups, the values are stored with 10 m vertical resolution and 1 nautical mile (NM) horizontal resolution. The procedure for allocation by species is based on:

- composition in trawl catches (pelagic and demersal hauls) - the appearance of the echo recordings

- inspection of target strength distributions - inspection of target frequency responses

For each trawl catch the relative s

-contribution from each species is calculated (Korsbrekke 1996) and used as a guideline for the allocation. In these calculations the fish length dependent catching efficiency of cod and haddock in the bottom trawl (Aglen and Nakken 1997) is taken into account. If the trawl catch gives the true composition of the species contributing to the observed s

value, those catch-based s

- proportions could be used directly for the allocation. In the scrutinizing process the scientists have to evaluate to what extent these catch-based s

-proportions are reasonable, or if they should be modified on the basis of knowledge about the fish behaviour and the catching performance of the gear.

Estimation procedures

The area is divided into rectangles of 1/2q latitude and 1q longitude. For each rectangle and each species an arithmetic mean s

is calculated for the demersal zone (less than 10 m above bottom) and the pelagic zone (more than 10 m above bottom). Each of those acoustic densities by rectangle are then converted to fish densities by the equation:

U

V

s (1)

U

is average fish density (number of fish / square NM) by rectangle s

is average acoustic density (square m / square NM) by rectangle V

is average backscattering cross-section (square NM) by rectangle

For cod, haddock and redfish the backscattering cross-section ( V ), target strength (TS) and fish length (L cm) is related by the equation (Foote, 1987):

TS

©¨ ·

¹¸ ˜

10 log 4 V 20 log( ) 68

S

(2)

Indices for the period 1981-1992 have been recalculated (Aglen and Nakken 1997) taking account of:

- changed target strength function

- changed bottom trawl gear (Godø and Sunnanå 1992)

- size dependant catching efficiency for cod and haddock (Dickson 1993a,b)

In 1999 the indices for cod and haddock were revised and some errors in the time series were discovered and corrected (Bogstad et al. 1999).

Combining equations 1 and 2 gives

U

5 021 10 . ˜

˜ s

/ L

(3)

L

is average squared fish length by rectangle and by depth channels (i.e., pelagic and bottom).

As a basis for estimating L

trawl catches considered to be representative for each rectangle

and depth zone are selected. This is a partly subjective process, and in some cases catches

from neighbouring rectangles are used. Only bottom trawl catches are used for the demersal

zone, while both pelagic and bottom trawl catches are applied to the pelagic zone. Length

frequency distributions by 1 cm length groups form the basis for calculating mean squared

length. The bottom trawl catches are normalised to 1 NM towing distance and adjusted for

length dependant fishing efficiency (Aglen and Nakken 1997, see below). Length

distributions from pelagic catches are applied unmodified. Since 2001 the post processing

program BEAM has been used for working out the acoustic estimates. This program provides

an automatic allocation of trawl samples to strata (rectangles). The automatic allocation is

modified by the user when considered necessary.

Let f

be the (adjusted) catch by length group i and let L

be the midpoint (cm) of the length interval i. Then:

L

f L

f

i i

i i i

i i i

i 2

˜

¦

¦

min max

min

max

(4)

For each species the total density ( U

) by rectangle and depth zone is now calculated by equation (3). This total density is then split on length groups according to the estimated length distribution. Next, these densities are converted to abundance by multiplying with the area of the rectangle. The abundance by rectangle is then summed for defined main areas (Figure 2.1). Estimates by length are converted to estimates by age using an age length key for each main area. The total biomass is estimated by multiplying the numbers at age by weight at age from the swept area estimates (see section 2.3).

2.2 Swept area measurements

All vessels were equipped with the standard research bottom trawl Campelen 1800 shrimp trawl with 80 mm (stretched) mesh size in the front. Prior to 1994 a cod-end with 35-40 mm (stretched) mesh size and a cover net with 70 mm mesh size were used. Since this mesh size may lead to considerable escapement of 1 year old cod, the cod-ends were in 1994 replaced by cod- ends with 22 mm mesh size. At present a cover net with 116 mm meshes is mostly used.

The trawl is now equipped with a rockhopper ground gear (Engås and Godø 1989). Until and including 1988 a bobbins gear was used, and the cod and haddock indices from the time period 1981-1988 have since been recalculated to ‘rockhopper indices’ and adjusted for length dependent fishing efficiency and/or sweep width (Godø and Sunnanå 1992, Aglen and Nakken 1997). The sweep wire length is 40 m, plus 12 m wire for connection to the doors.

In the Norwegian shrimp survey (Aschan and Sunnanå 1997) the Campelen trawl has been rigged with some extra floats (45 along the ground rope and 18 along the under belly and trunk, all with 20mm diameter) to reduce problems on very soft bottom. This rigging has been referred to as “Tromsø rigging”. When the shrimp survey was terminated 2004 and later merged with the Ecosystem survey in 2005, improved shrimp data were also requested from the winter survey, and the “Tromsø rigging” was used in parts of the shrimp areas in 2004 (11 stations) and 2005 (9 stations). Since 2006 the “Tromsø rigging” has been used for nearly all bottom trawl stations taken by Norwegian vessels in the winter survey.

Vaco doors (6 m

, 1500kg), were previously standard trawl doors on board the Norwegian

research vessels. On the Russian vessels and hired vessels V-type doors (ca 7 m

) have been

used. In 2004, R/V “Johan Hjort” changed to a V-type door (Steinshamn W-9, 7.1m

, 2050

kg), the same type as used on the Russian research vessels. In 2010 the V-doors were replaced

by 125” Thyborøn trawl doors. R/V “Helmer Hanssen” has used Thyborøn trawl doors since the 2008 survey.

In order to achieve constant sampling width of a trawl haul independent of e.g. depth and wire length, a 10-14 m rope “locks” the distance between the trawl wires 80-150 m in front of the trawl doors on the Norwegian vessels. This is called “strapping”. The distance between the trawl doors is then in most hauls restricted to the range 48-52 m regardless of depth (Engås and Ona 1993, Engås 1995). Strapping was first attempted in the 1993 survey on board one vessel, in 1994 it was used on every third haul and in 1995-1997 on every second haul on all vessels. Since 1998 it has been used on all hauls when weather conditions permitted.

Strapping is not applied on the Russians vessels, but the normal distance between the doors is about 50 m (D. Prozorkevich, pers. comm.).

Standard tow duration is now 15 minutes (until 1985 the tow duration was 60 min. and from 1986 to 2010 30 min). Trawl performance is constantly monitored by Scanmar trawl sensors, i.e., distance between the doors, vertical opening of the trawl and bottom contact control. In 2005-2008 sensors monitoring the roll and pitch angle of the doors were used due to problems with the Steinshamn W-9 doors. The data is logged on files, but have so far not been used for further evaluation of the quality of the trawl hauls.

The positions of the trawl stations are pre-defined. When the swept area investigations started

in 1981 the survey area was divided into four main areas (A, B, C and D, Fig 2.1) and 35

strata.

During the first years the number of trawl stations in each stratum was set based on expected fish distribution in order to reduce the variance, i.e., more hauls in strata where high and variable fish densities were expected to occur. During the 1990s trawl stations have been spread out more evenly, yet the distance between stations in the most important cod strata is shorter (16 or 20 NM) compared to the less important strata (24, 30 or 32 NM). During the 1990s considerable amounts of young cod were distributed outside the initial four main areas, and in 1993 the investigated area was therefore enlarged by areas D’, E, and the ice-free part of Svalbard (S) (Fig. 2.1 and Table 3.5), 28 strata altogether. In the 1993-1995 survey reports, the Svalbard area was included in A’ and the western (west of 30qE) part of area E. Since 1996 a revised strata system with 23 strata has been used (Figure 2.1). The main reason for reducing the number of strata was the need for a sufficient number of trawl stations in each stratum to get reliable estimates of density and variance. In later years a few pre-defined trawl stations have been performed north of the strata system due to increased abundance of cod in these areas, and in 2014 the investigated area was enlarged by three new strata in northwest, 24-26 (main area N, Fig. 2.1). However, the data are so far not included in the estimation of standard abundance indices.

Swept area fish density estimation

Swept area fish density estimates ( U

) by species (s) and length (l) were estimated for each bottom trawl haul by the equation:

l s

l s l

s

a

f

, ,

U

l

U

number of fish of length l per n.m.

observed on trawl station s

l

f

estimated frequency of length l

l

a

swept area:

,

1852

l s l s

EW

a d ˜

d

towed distance (nm)

EW

length dependent effective fishing width:

D l

EW

˜ for l

l l

lmin

l

EW

EW = D ˜ l

for l d l

lmax

l

EW

EW = D ˜ l

for l t l

The parameters are given in the text table below:

Species DD EE ^lmin l_max

Cod 5.91 0.43 15 cm 62 cm

Haddock 2.08 0.75 15 cm 48 cm

The fishing width was previously fixed to 25 m = 0.0135 nm. Based on Dickson (1993a,b), length dependent effective fishing width for cod and haddock was included in the calculations in 1995 (Korsbrekke et al., 1995). Aglen and Nakken (1997) have adjusted both the acoustic and swept area time series back to 1981 for this length dependency based on mean-length-at- age information. In 1999, the swept area 1983-1995 time series was recalculated for cod and haddock using the new area and strata divisions (Bogstad et al. 1999).

For redfish, Greenland halibut and other species, a fishing width of 25 m was applied, independent of fish length.

For each station, s, observations of fish density by length ( U

) is summed in 5 cm length- groups. Stratified indices by length-group and stratum will then be:

¦

˜

p s

l s p

p l

p

S

L A

stratum in

,

,

U

L

index, stratum p, length-group l

A

area (n.m.

) of stratum p (or the part of the stratum covered by the survey) S

number of trawl stations in stratum p

The coverage of the most northern and most eastern strata differs from year to year. The areas of these strata are therefore calculated according to the coverage each year (Table 3.5).

Indices are estimated for each stratum within the main areas A, B, C, D, D’, E and S. Total number of fish in each 5 cm length group in each main area is estimated by adding the indices of all strata within the area. Total number of fish at age is estimated by using an age-length key constructed for each main area. Total indices on length and age are estimated adding the values for all main areas.

2.3 Sampling of catch and age-length keys.

Sorting, weighing, measuring and sampling of the catch are done according to instructions

given in Mjanger et al. (2014). Since 1999 all data except age are recorded electronically by

otoliths were sampled from one specimen per 5 cm length-group. Regarding the redfish species, Sebastes norvegicus and S. mentella, otoliths for age determination were sampled from two fish in every 5 cm length-group on every station. Greenland halibut were sorted by sex before length measurement and otolith sampling. From this species otoliths were collected from 5 fish per 5 cm length group for each sex on all stations. Table 3.4 gives an account of the sampled material.

An age-length key is constructed for each main area. All age samples are included and weighted according to:

w L

p l

n

p l p l ,

, , l

w

- weighting factor

l

L

- swept area index of number fish in length-group l in stratum p n

- number of age samples in length-group l and stratum p

Fractions are estimated according to:

P

n w

n w

a l

p a l p l

p

p l p l

p ( )

, , ,

, ,

˜

˜

¦

¦

p

- weighted fraction of age a in length-group l and stratum p

n

- number of age samples of age a in length-group l and stratum p

Number of fish by age is then estimated following the equation:

N

L

P

l p

¦ ˜

¦

Mean length and –weight by age is then estimated according to (only shown for weight):

W

W w

a

w

a p l j p l j

l p

p l j l p

¦ ˜

¦

¦

¦

¦

¦

, , , ,

,

W

- weight of sample j in length-group l, stratum p and age a

3 Survey operation and material

Table 3.1 presents the vessels participating in the survey in 2013 – 2014 and IMR trawl station series numbers. Catch data and biological samples from the Russian vessels were converted to the IMR SPD-format. The acoustic data from the Russian vessels was reported to IMR as allocated values by species at 5 nm intervals, split on a bottom layer (<10m from bottom) and a pelagic layer (>10m above bottom).

Table 3.1. Norwegian and Russian vessel participation by time period and Norwegian trawl station series numbers by vessel for the winter surveys 2013-2014.

Vessel

Year

2013 2014

Period Series no. Period Series no.

Johan Hjort 01.02-14.03 70001-70187 31.01-11.03 70001-70196

Helmer Hanssen 22.01-02.03 70301-70490

Fridtjof Nansen 30.01-17.02 00001-00113

Vilnyus 08.02-02.03 00001-00128

Table 3.2 presents the number of swept area trawl stations, other bottom trawl stations and pelagic trawl stations taken in the different main areas. For the calculation of swept area indices, only the successful pre-defined bottom trawl stations within the strata system were used. The number of stations in the new strata 24-26 are also given. Table 3.3 gives an account of the sampled length- and age material from bottom hauls and pelagic hauls. Figure 3.1 shows survey tracks and trawl stations for each survey in 2013-2014.

Figure 3.1. Survey tracks and all trawl stations in the winter survey 2013-2014. Data source for the monthly ice

Table 3.2. Number of trawl stations by main area in the Barents Sea winter 2013-2014. B₁= swept area bottom trawl (quality=1 and condition<3), B₂=other bottom trawl, P=pelagic trawl, N=trawl stations in new strata.

Main area Trawl type

Year

2013 2014

A B₁

B₂ P

28 2 3

50 1 1

B B₁

B₂ P

23 6 -

30 4 2

C B₁

B₂ P

21 - -

24 - 3

D B₁

B₂ P

112 1 3 -

137 - 1

D' B₁

B₂ P

55 - -

67 1 -

E B1

B₂ P

15 - 2

33 - 1

S B₁

B₂ P

43 - 1

66 - 3 Inside strata system

B₁ B₂ P

297 9 9

407 6 11

N B

P

- -

73 2

Total B+B₁+B2

P

306 9

486 13

Table 3.3. Number of fish measured for length (L) and age (A) in the Barents Sea winter 2013-2014.

Year Cod Haddock S .marinus S. mentella Greenland

halibut

Blue whiting

L A L A L A L A L L

2013 14525 2451 19142 1671 479 156 6087 923 263 1091

2014 22624 4501 35940 2586 563 276 9310 1734 444 1846

Table 3.4. Area (NM²) covered in the bottom trawl surveys in the Barents Sea winter 1981-2014.

Main Area Sum Added

Year A B C D D' E S ABCD Total area

1981-92 23299 8372 5348 51116 - - - 88135 88135

1993 23929 8372 5348 51186 23152 8965 16690 88835 137642 1994 27131 8372 5348 51186 24975 12576 14252 92037 143840 1995 27131 8372 5348 51186 56822 14859 22836 92037 186554 1996 25935 9701 5048 53932 53247 5818 11600 94616 165281

1997¹ 27581 9701 5048 23592 2684 1954 16989 65922 87549 56200 1998¹ 27581 9701 5048 23592 5886 3819 23587 65922 99214 51100 1999 27581 9701 5048 43786 7961 5772 18470 86116 118319

2000 27054 9701 5048 52836 28963 14148 24685 94639 162435 2001 26469 9701 5048 53932 29376 15717 23857 95150 164100 2002 26483 9701 5048 53932 21766 15611 24118 95165 156659 2003 26483 9701 5048 52805 23506 6185 22849 94038 146578 2004 27976 9845 5162 53567 42903 4782 20415 96549 164649 2005 27581 9701 5048 53932 38716 19720 24194 96263 178893

2006² 27581 9701 5048 53932 34980 13687 24194 96263 169123 18100 2007¹ 27581 9701 5048 23428 8420 20621 27416 65759 122216 56700 2008 27581 9701 5048 53932 23711 18557 25905 96263 164436

2009 27581 9701 5048 53932 31691 15505 27416 96263 170874 2010 27581 9701 5048 53932 17896 18330 27416 96263 159904 2011 27581 9701 5048 53932 32937 16467 27416 96263 173082

2012² 27581 9701 5048 53932 9831 16970 27416 96263 150480 16700 2013 27581 9701 5048 53932 57598 20818 27416 96263 202095

2014³ 27581 9701 5048 53932 54464 29692 27416 96263 207835

1REZ not covered

2REZ(Murman coast and Area D’ in 2006 and Area D’ in 2012) not completely covered

3 Additional northern areas covered; ca 62 000 NM², not included in standard survey index calculations

Table 3.5. Degree of coverage and main reasons for incomplete coverage in the Barents Sea winter 1981-2014.

Year Coverage Comments

1981-1992 ABCD 1993-1996 ABCDD’ES

1997 NEZ, S Not allowed access to REZ

1998 NEZ, S, minor part of REZ Not allowed access to most of REZ

1999 ABCDD’ES Partly limited coverage due to westerly ice extension

2000 ABCDD’ES

2001-2005 ABCDD’ES Russian vessel covered where Norwegians had no access 2006 ABCDD’ES Not access to Murman coast, no Russian vessel

2007 NEZ, S Not allowed access to REZ, no Russian vessel

2008 ABCDD’ES Russian vessel covered where Norwegians had no access

4 Hydrography

The standard hydrographical sections ”Fugløya-Bjørnøya” and “Vardø-Nord” are taken during the later part of the surveys. Figure 4.1 shows the observed mean temperature at 50- 200 m depth for the period 1977-2014. Both time series show an increasing trend. The increases in temperatures are approximately 0.44 (”Fugløya-Bjørnøya”) and 0.51 (“Vardø- Nord”) °C per decade. Unfortunately, the time series have some missing values.

5 Total echo abundance of cod and haddock

Table 5.1 presents the time series of total echo abundance (echo density multiplied by area) of cod and haddock in the investigated areas. Since 1993 the acoustic values have been split between the two species during the scrutinizing. The values for cod have showed an increasing trend since the mid 2000s, with a peak in 2013. The values for haddock increased gradually from the end of the 1990s to 2009, and have decreased somewhat in the later years.

The fraction of the total echo abundance recorded in the bottom layer has been somewhat lower in later years for cod compared to the mid 2000s. For haddock this fraction is lower than for cod and more stable over the time series.

Figures 5.1 and 5.2 present the distribution of total echo abundance by estimation rectangles in 2013-2014 for cod and haddock, respectively. The 2014 maps show distributions north of the swept area strata, probably extending even further north.

Figure 4.1. Mean temperatures in 50-200 m depth in 1977-2014.

A) "Fugløya-Bjørnøya" in March, B) "Vardø-Nord" in March.

Table 5.1. Cod and haddock. Total echo abundance and echo abundance in the 10 m layer above the bottom in the Barents Sea winter 1981-2014 (m² reflecting surface · 10^-3). 1981 - 1992 includes only mainly areas A, B, C and D.

Total Bottom Bottom/total

Year Cod Haddock Sum Cod Haddock Sum Cod Haddock Sum

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996

3905 5076 4125 2729

2854 3650 3051 1556

2097 686 597 2284 5187 5990 2676 1696 914 1355 2706 4128 6759 8726 7176 4285

1011 1201 1525 1004

548 609 651 626

799 311 169 604 736 820 608 579 308 536 803 951 1559 1810 2176 1630

0.26 0.24 0.37 0.37

0.19 0.17 0.21 0.40

0.38 0.45 0.28 0.26 0.14 0.14 0.23 0.34 0.34 0.40 0.30 0.23 0.23 0.21 0.30 0.38 1997¹

1998¹

1354 2406

995 581

2349 2987

530 632

258 143

788 775

0.39 0.26

0.26 0.29

0.34 0.26

1999 1364 704 2068 389 145 534 0.29 0.21 0.26

2000 2596 1487 4083 610 343 953 0.23 0.23 0.23

2001 2002

2085 1943

1440 2329

3525 4272

698 627

615 477

1313 1104

0.34 0.32

0.43 0.20

0.37 0.26

2003 3699 3398 7097 1248 753 2001 0.34 0.22 0.28

2004 1162 1985 3147 576 626 1202 0.50 0.32 0.38

2005 1299 2873 4172 457 940 1397 0.35 0.33 0.33

2006 1195 2755 3950 462 697 1159 0.39 0.25 0.29

2007^1,2 681 2515

2008 3636 5981 9617 958 1306 2264 0.26 0.22 0.24

2009 2010 2011 2012 2013 2014

2513 3712 3044 3762 5105 4722

6326 5905 3790 4157 4078 3176

8839 9617 6834 7919 9183 7898

806 1014

823 1028 1364 926

1280 1186

864 810 1031

529

2086 2200 1687 1838 2395 1455

0.32 0.27 0.27 0.27 0.27 0.20

0.20 0.20 0.22 0.19 0.25 0.17

0.24 0.23 0.25 0.23 0.26 0.18

1not scaled for uncovered areas

2 not possible to split on bottom and total due to LSSS settings

Figure 5.1. COD. Distribution of total echo abundance winter 2013-2014. Unit is s_A per square nautical mile (m²/n.mile²). Swept area strata and main areas (thick line) in red.

Figure 5.2. HADDOCK. Distribution of total echo abundance winter 2013-2014. Unit is s_A per square nautical mile (m²/n.mile²). Swept area strata and main areas (thick line) in red.

6 Distribution and abundance of cod

6.1 Acoustic estimation

Surveys in the Barents Sea at this time of the year mainly cover the immature part of the cod stock. Most of the mature cod (age 7 and older) have started on their spawning migration southwards out of the investigated area, and are therefore covered to a lesser extent. There are indications that a higher proportion than normal spawned along Finnmark in some of the recent years, e.g. 2004-2006. Thereby a higher proportion of the spawners might have been covered by the survey these years.

Table 6.1 shows the acoustic indices for each age group by main areas in 2013-2014. The time series (1981-2014) is presented in Table 6.2. The estimates have been variable and increasing in later years, with a peak in 2013, and this may partly be explained by variable and not complete coverage of the distribution area towards north and east in several years. As cod grow older, their distribution shifts more south-westerly during winter, and they it so to say “grows” into the incomplete survey. This is especially evident for the strong 2004 and 2005 year-classes, which as 6-7 year olds stand out as the strongest in the time series. Of more recent year-classes the 2011 year-class seems to be strong.

Table 6.1. COD. Acoustic abundance for the main areas of the Barents Sea winter 2013-2014 (numbers in millions).

Area Year

Age group

Total

Biomass ('000 t) 1 2 3 4 5 6 7 8 9 10+

A 2013

2014

30.7 13.5

4.9 3.9

5.9 10.4

9.9 8.6

8.1 10.2

8.1 8.0

17.3 3.6

27.0 17.2

10.4 14.3

3.6 2.4

125.9 92.2

271.1 207.4

B 2013

2014

0.2 3.6

0.2 0.8

1.0 12.9

2.3 6.6

6.7 16.6

12.9 15.2

26.7 7.0

35.6 28.5

42.1 21.3

6.0 15.3

133.6 127.8

587.9 428.9

C 2013

2014

6.6 2.8

0.7 0.7

1.0 3.3

2.7 2.2

1.9 3.5

0.9 2.5

2.1 2.3

5.4 6.4

3.1 6.3

0.6 1.0

24.9 31.0

57.4 100.5

D 2013

2014

264.4 140.5

47.3 41.7

31.2 42.0

33.3 26.6

35.5 23.7

18.1 19.1

24.1 10.9

41.4 13.0

10.6 14.0

1.8 4.3

507.7 335.8

427.2 277.2

D' 2013

2014

97.7 89.9

35.2 40.2

15.3 56.6

14.4 39.2

4.7 13.1

3.4 8.4

3.6 5.4

4.0 1.3

0.9 2.3

-

0.2 256.7 84.3

E ²⁰¹³

2014

48.0 218.0

14.0 29.7

4.1 57.1

12.5 19.4

4.6 8.3

2.9 3.4

2.8 3.1

3.0 3.5

1.0 0.9

0.3 2.1

93.2 345.6

48.5 82.7

S ²⁰¹³

2014

23.0 161.9

8.4 22.1

5.7 37.6

9.8 15.2

9.3 16.1

5.4 8.5

9.5 5.2

7.4 7.4

2.1 4.0

0.2 0.8

80.6 278.6

86.7 119.8 ABCD 2013

2014

301.8 160.4

53.1 47.1

39.0 68.6

48.2 44.0

52.2 54.0

40.0 44.8

70.1 23.8

109.4 65.1

66.2 55.9

12.0 23.0

792.1 586.8

1344 1014 Total ²⁰¹³

2014

470.6 630.1

110.8 139.1

64.1 220.0

85.0 117.8

70.8 91.5

51.7 65.1

86.0 37.5

123.8 77.3

70.1 63.2

12.4 26.0

1145.3 1467.7

1536 1301

Table 6.2. COD. Abundance indices from acoustic surveys in the Barents Sea winter 1981-2014 (numbers in millions). 1981-1992 includes only main areas A, B C and D. Observations outside main areas A-S not included.

Age Biomass

Year 1 2 3 4 5 6 7 8 9 10+ Total (‘000 t)

1981 8.0 82.0 40.0 63.0 106.0 103.0 16.0 3.0 1.0 1.0 423.0 595 1982 4.0 5.0 49.0 43.0 40.0 26.0 28.0 2.0 0.0 0.0 197.0 303 1983 60.5 2.8 5.3 14.3 17.4 11.1 5.6 3.0 0.5 0.1 120.5 111 1984 745.4 146.1 39.1 13.6 11.3 7.4 2.8 0.2 0.0 0.0 966.0 134 1985 69.1 446.3 153.0 141.6 19.7 7.6 3.3 0.2 0.1 0.0 840.9 392 1986 353.6 243.9 499.6 134.3 65.9 8.3 2.2 0.4 0.1 0.0 1308.2 503 1987 1.6 34.1 62.8 204.9 41.4 10.4 1.2 0.2 0.7 0.0 357.3 207 1988 2.0 26.3 50.4 35.5 56.2 6.5 1.4 0.2 0.0 0.0 178.4 99 1989 7.5 8.0 17.0 34.4 21.4 53.8 6.9 1.0 0.1 0.1 150.1 155 1990 81.1 24.9 14.8 20.6 26.1 24.3 39.8 2.4 0.1 0.0 234.1 246 1991 181.0 219.5 50.2 34.6 29.3 28.9 16.9 17.3 0.9 0.0 578.7 418 1992 241.4 562.1 176.5 65.8 18.8 13.2 7.6 4.5 2.8 0.2 1092.9 405 1993 1074.0 494.7 357.2 191.1 108.2 20.8 8.1 5.0 2.3 2.5 2264.0 753 1994 858.3 577.2 349.8 404.5 193.7 63.6 12.1 3.7 1.7 0.9 2465.4 950 1995 2619.2 292.9 166.2 159.8 210.1 68.8 16.7 2.1 0.7 1.0 3537.4 713 1996 2396.0 339.8 92.9 70.5 85.8 74.7 20.6 2.8 0.3 0.4 3083.8 450 1997¹ 1623.5 430.5 188.3 51.7 49.3 37.2 22.3 4.0 0.7 0.1 2407.5 322 1998¹ 3401.3 632.9 427.7 182.6 42.3 33.5 26.9 13.6 1.7 0.3 4762.8 506 1999 358.3 304.3 150.0 96.4 45.1 10.3 6.4 4.1 0.8 0.3 976.0 224 2000 154.1 221.4 245.2 158.9 142.1 45.4 9.6 4.7 3.0 1.1 985.4 481 2001 629.9 63.9 138.2 171.6 77.3 39.7 11.8 1.4 0.5 0.2 1134.7 408 2002 18.2 215.5 69.3 112.2 102.0 47.0 18.0 3.0 0.4 0.3 585.9 416 2003 1693.9 61.5 303.4 114.4 129.0 114.9 34.3 7.7 1.9 0.5 2461.5 731 2004 157.6 105.2 33.6 92.8 30.7 27.6 17.0 5.9 1.2 0.2 471.8 241 2005 465.3 119.6 123.9 33.7 62.8 16.9 14.5 4.2 1.0 0.4 842.4 249 2006²

2007¹ 2008 2009 2010 2011 2012²

544.6 125.0 68.8 321.5 485.4 389.4 950.6

216.6 61.7 97.6 30.6 59.4 124.8 72.7

79.8 80.3 210.2 182.6 34.7 47.1 133.9

59.1 37.1 306.1 178.3 121.9 29.1 52.7

15.5 30.4 140.6 137.1 174.7 80.4 37.7

25.6 9.1 69.4 35.0 162.3 107.7 69.4

8.8 14.1 21.6 12.5 44.4 105.4 126.1

4.5 5.0 12.2 5.2 13.8 17.1 77.0

1.4 2.1 3.1 3.7 3.5 4.5 10.4

0.5 0.7 0.8 0.9 3.5 3.0 6.0

956.5 365.6 930.4 907.3 1103.6 908.6 1536.4

222 198 846 541 932 777 1030 2013 470.6 110.8 64.1 85.0 70.8 51.7 86.0 123.8 70.1 12.4 1145.3 1536 2014 630.1 139.1 220.0 117.8 91.5 65.1 37.5 77.3 63.2 26.0 1467.7 1301

1 Indices raised to also represent the Russian EEZ.

2Indices raised to also represent uncovered parts of the Russian EEZ’.

6.2 Swept area estimation

Figures 6.1 - 6.4 show the geographic distribution of bottom trawl catch rates (number of fish per NM

, for cod size groups ” 19 cm, 20-34 cm, 35-49 cm and • 50 cm. As in previous years, a high proportion of the smallest cod (less than 35 cm) were found in the eastern part of the survey area within the Russian EEZ and near the northern borders of the standard strata system (strata 1-23). In 2014 a higher proportion of cod ” 19 cm were found in the extended survey area (strata 24-26) than in the rest of the survey area (Table 6.3). These size groups have probably been largely underestimated in earlier years. Mehl et al. (2013) found that since 2009 more of the largest cod had been found in the north-western part of the survey area (main area S), and this trend is confirmed by the 2013 and 2014 estimates.

Figure 6.1. COD ” 19 cm. Distribution in valid bottom trawl catches winter 2013-2014 (number per nm²). Zero catches are indicated by black points.

Figure 6.3. COD 35-49 cm. Distribution in valid bottom trawl catches winter 2013-2014 (number per nm²).

Zero catches are indicated by black points.

Figure 6.4. COD • 50 cm. Distribution in valid bottom trawl catches winter 2013-2014 (number per nm²). Zero catches are indicated by black points.

Table 6.3 presents the distribution of the indices by main areas and age and the whole time

series (1981-2014) is shown in Table 6.4. Also the bottom trawl indices have fluctuated

somewhat due to the same reasons as for the acoustic indices, and the 2004 and 2005 year-

classes at the moment stand out as the strongest in the time series. Both the 2009 and 2011

year-classes seemed to be strong as 1-year olds, but the 2009 year-class was reduced to below

average level at age 3. A considerable amount of cod was found in the extended survey area

(Table 6.3), on average over all age groups about 76 % of the amount found in the standard

survey area by numbers and about 15 % by biomass.

Table 6.3. COD. Abundance indices from bottom trawl hauls for main areas of the Barents Sea winter 2013- 2014 (numbers in millions.).

Area Year

Age group Total Biomass

1 2 3 4 5 6 7 8 9 10+ ('000 t)

A 2013

2014

9.4 5.9

2.5 2.0

3.0 6.1

4.6 6.1

4.5 6.3

4.3 4.6

9.5 1.4

14.1 5.4

4.0 3.8

1.2 1.0

57.0 42.6

132.6 78.9

B 2013

2014

0.1 0.6

0.2 0.2

0.4 4.1

0.9 2.3

2.8 5.2

2.9 4.1

7.5 3.0

11.9 9.4

7.8 6.5

1.2 4.2

35.6 39.6

149.0 133.6

C 2013

2014

2.3 1.1

0.3 0.3

0.4 1.3

1.0 1.2

0.7 1.4

0.3 1.3

0.8 1.1

2.2 2.9

1.2 3.3

0.2 0.6

9.3 14.5

21.8 48.7

D 2013

2014

190.1 104.3

32.0 52.5

20.8 35.7

23.7 20.3

24.0 18.2

12.0 17.7

18.9 8.1

28.9 11.1

7.7 10.8

1.4 3.4

359.5 282.1

299.8 225.7

D' 2013

2014

101.3 114.8

81.6 40.4

29.4 40.6

34.0 22.8

10.4 8.9

4.3 7.3

8.6 4.1

9.4 3.5

2.6 3.0

0.2 0.4

281.8 245.8

125.9 85.4

E 2013

2014

58.9 105.0

33.8 30.9

10.6 43.3

24.2 12.6

5.5 6.5

3.1 1.8

2.8 2.2

3.6 2.0

1.0 0.9

0.3 0.5

143.8 205.7

60.7 50.8

S 2013

2014

37.5 167.4

13.7 26.3

9.2 43.2

21.6 18.4

17.4 20.4

8.4 11.5

13.2 7.9

9.2 9.8

2.9 4.9

- 0.9

133.0 310.7

129.1 154.3 ABCD 2013

2014

201.8 111.9

34.9 55.0

24.5 47.2

30.2 29.9

32.0 31.1

19.6 27.7

36.7 13.6

57.0 28.8

20.7 24.4

4.0 9.2

461.4 378.8

603 490 Total 2013

2014

399.5 499.1

164.1 152.4

73.8 174.2

110.0 83.7

65.3 66.8

35.4 48.3

61.3 27.7

79.3 44.2

27.2 33.1

4.6 10.3

1021 1140

919 780 Additional areas

2014 724.4 45.7 49.2 14.0 17.6 10.0 1.4 5.9 3.3 0.4 872 116 Additional areas/

standard areas (%) 145 30 28 17 26 21 5 13 10 4 76 15

Table 6.4. COD. Abundance indices from bottom trawl surveys in the Barents Sea winter 1981-2014 (numbers in millions). 1981-1992 includes only main areas A, B, C and D. Observations outside main areas A-S not included.

Age Biomass

Year 1 2 3 4 5 6 7 8 9 10+ Total (‘000 t)

1981 4.6 34.3 16.4 23.3 40.0 38.4 4.8 1.0 0.3 0 163 203 1982 0.8 2.9 28.3 27.7 23.6 15.5 16.0 1.4 0.2 0 116 174 1983 152.9 13.4 25.0 52.3 43.3 17.0 5.8 3.2 1.0 0.1 314 220 1984 2755.0 379.1 97.5 28.3 21.4 11.7 4.1 0.4 0.1 0.1 3298 310 1985 49.5 660.0 166.8 126.0 19.9 7.7 3.3 0.2 0.1 0.1 1034 421 1986 665.8 399.6 805.0 143.9 64.1 8.3 1.9 0.3 0 0 2089 639 1987 30.7 445.0 240.4 391.1 54.3 15.7 2.0 0.5 0 0 1180 398 1988 3.2 72.8 148.0 80.5 173.3 20.5 3.6 0.5 0 0 502 285 1989 8.2 15.6 46.4 75.9 37.8 90.2 9.8 0.9 0.1 0.1 285 271 1990 207.2 56.7 28.4 34.9 34.6 20.6 27.2 1.6 0.4 0 412 246 1991 460.5 220.1 45.9 33.7 25.7 21.5 12.2 12.7 0.6 0 833 352 1992 126.6 570.9 158.3 57.7 17.8 12.8 7.7 4.3 2.7 0.2 959 383 1993 534.5 420.4 273.9 140.1 72.5 15.8 6.2 3.9 2.2 2.4 1472 565 1994 1035.9 535.8 296.5 310.2 147.4 50.6 9.3 2.4 1.6 1.3 2391 761 1995 5253.1 541.5 274.6 241.4 255.9 76.7 18.5 2.4 0.8 1.1 6666 943 1996 5768.5 707.6 170.0 115.4 137.2 106.1 24.0 2.9 0.4 0.5 7033 701 1997¹

1

4815.5 1045.1 238.0 64.0 70.4 52.7 28.3 5.7 0.9 0.5 6321 495 1998¹ 2418.5 643.7 396.0 181.3 36.5 25.9 17.8 8.6 1.0 0.5 3730 429 1999 484.6 340.1 211.8 173.2 58.1 13.4 6.5 5.1 1.2 0.4 1294 318 2000 128.8 248.3 235.2 132.1 108.3 26.9 4.3 2.0 1.2 0.4 888 356 2001 657.9 76.6 191.1 182.8 83.4 38.2 8.9 1.1 0.4 0.2 1241 428 2002 35.3 443.9 88.3 135.0 109.6 42.5 15.1 2.4 0.3 0.2 873 441 2003 2991.7 79.1 377.0 129.7 91.1 67.3 18.3 4.9 1.0 0.2 3760 546 2004 328.5 235.4 76.6 172.5 56.9 44.7 27.3 7.6 1.7 0.4 952 413 2005 824.3 224.6 246.9 62.1 98.1 24.7 15.5 4.5 1.1 0.4 1502 355 2006² 862.7 288.4 118.1 111.5 28.7 43.7 10.2 4.9 1.4 0.6 1470 335 2007¹ 485.9 393.9 367.7 85.0 62.9 14.8 17.9 4.8 1.8 0.7 1435 397 2008 70.4 92.1 190.2 333.6 91.0 47.2 13.0 8.8 2.0 0.4 849 684 2009 382.7 39.1 118.3 219.6 193.9 58.6 19.6 6.8 4.9 0.9 1044 738 2010 1020.2 104.4 36.0 106.9 160.8 140.7 40.0 11.9 3.5 2.2 1627 814 2011 618.6 223.0 88.1 54.1 122.1 139.9 95.6 16.8 3.9 2.4 1365 874 2012² 1364.0 329.9 98.0 68.4 44.8 87.3 124.1 53.1 7.9 4.8 2182 910 2013 399.5 164.1 73.8 110.0 65.3 35.4 61.3 79.3 27.2 4.6 1021 919 2014 499.1 152.4 174.2 83.7 66.8 48.3 27.7 44.2 33.1 10.3 1140 780 1 Indices raised to also represent the Russian EEZ.

2 Indices raised to also represent uncovered parts of the Russian EEZ.

6.3 Growth and survey mortalities

Tables 6.5 and 6.6 present the time series for mean length (1981-2014) and mean weight (1983-2014) at age for the entire standard area. Weights and lengths at age were fairly low in the period 1995-2000, but increased somewhat in 2001. Since then there has been moderate fluctuations, but with a slight decreasing trend for older fish (6+) in later year. The same pattern is reflected in the annual weight increments (Table 6.7).

Table 6.8 gives the time series of survey based mortalities (log ratios between survey indices of the same year class in two successive years) since 1993. These mortalities are influenced by natural and fishing mortality, age reading errors, and the catchability and availability (coverage) at age for the survey. In the period 1993-1999 there was an increasing trend in the survey mortalities. The trend appears most consistent for the age groups 3-7 in the swept area estimates. Most later surveys show lower mortalities, but there are some fluctuations for the same reasons as mentioned for the acoustic and swept area indices. Presumably the mortality of the youngest age groups (ages 1-3) is mainly caused by predation, while for the older age groups it is mainly caused by the fishery. Before 2001 the survey mortalities for age 4 and older were well above the mortalities estimated in the ICES assessment. Decreasing survey catchability at increasing age could be one reason for this. Another possible reason could be that the assessment does not include all sources of mortality, like discards, unreported catches, or poorly quantified predation. The low survey mortalities in the most recent years, even with

“impossible” negative values, could partly be caused by fish gradually “growing into” the

covered area at increasing age. The observed mortality rates in the acoustic investigations

have been more variable. This might be caused by changes in fish behaviour and how

available the fish is for acoustic registration.

Table 6.5. COD. Length (cm) at age in the Barents Sea from the investigations winter 1981 - 2014. Observations outside main areas A-S not included.

Age

Year 1 2 3 4 5 6 7 8

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997¹ 1998¹ 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012¹ 2013 2014

17.0 14.8 12.8 14.2 16.5 11.9 13.9 15.3 12.5 14.4 13.6 13.2 11.3 12.0 12.7 12.6 11.4 10.9 12.1 13.0 12.0 12.2 12.0 11.0 11.5 12.2 13.4 12.5 11.7 11.4 12.5 11.8 11.4 10.4

26.1 25.8 27.6 28.4 23.7 21.6 21.0 23.3 25.4 27.9 27.2 23.9 20.3 18.3 18.7 19.6 18.8 17.4 18.8 21.0 22.5 19.9 21.2 18.9 18.6 19.9 21.3 22.3 21.4 19.1 19.9 18.6 20.1 18.4

35.5 37.6 34.8 35.8 40.3 34.4 31.8 29.7 34.7 39.4 41.6 41.3 35.9 30.5 29.9 28.1 28.0 28.7 29.0 28.7 33.1 30.1 29.1 32.0 29.3 31.3 30.7 32.5 32.2 31.2 30.3 28.2 31.6 29.7

44.7 46.3 45.9 48.6 48.7 49.9 41.3 38.7 39.9 47.1 51.7 49.9 50.8 44.7 42.0 41.0 40.4 40.0 40.6 39.7 41.6 43.6 39.2 40.9 43.0 42.1 42.2 43.7 43.2 42.3 42.3 41.3 41.2 41.3

52.0 54.7 54.5 56.6 61.3 59.8 56.3 47.6 46.8 53.8 59.5 60.2 59.0 55.4 54.1 49.3 49.9 50.5 50.6 51.5 52.2 52.2 53.3 52.0 51.1 53.5 52.8 52.4 53.6 52.0 51.4 51.3 52.0 52.0

61.3 63.1 62.7 66.2 71.1 69.4 66.3 56.8 56.2 60.6 67.1 68.4 68.2 64.3 64.1 61.4 59.3 58.9 59.9 61.6 63.1 61.7 61.6 61.8 60.3 60.8 62.3 63.6 63.3 61.3 60.8 59.0 62.2 60.9

69.6 70.8 73.1 74.1 81.2 80.3 77.6 71.7 67.0 68.2 72.3 76.1 76.8 73.5 74.8 72.2 69.1 67.5 70.3 70.5 71.2 71.6 70.3 69.0 71.1 68.9 70.5 71.6 76.0 70.5 68.6 67.1 69.9 69.9

77.9 82.9 78.6 79.7 85.7 93.8 87.9 79.4 83.3 79.2 77.6 82.8 85.8 82.4 80.6 85.3 80.6 76.3 78.0 75.7 79.2 79.1 80.7 79.0 78.4 77.7 77.9 80.8 84.4 80.6 78.3 75.2 76.7 77.1 1Adjusted lengths

Table 6.6. COD. Weight (g) at age in the Barents Sea from the investigations winter 1983-2014. Observations outside main areas A-S not included.

Year \ Age 1 2 3 4 5 6 7 8 9 10 11 12

1983 20 190 372 923 1597 2442 3821 4758

1984 23 219 421 1155 1806 2793 3777 4566

1985 20 171 576 1003 2019 3353 5015 6154

1986 20 119 377 997 1623 2926 3838 7385

1987¹ 21 65 230 490 1380 2300 3970 6000

1988 24 114 241 492 892 1635 3040 4373

1989 16 158 374 604 947 1535 2582 4906 10943 5226

1990 26 217 580 1009 1435 1977 2829 4435 10772 11045 9615 1991 18 196 805 1364 2067 2806 3557 4502 7404 13447

1992 20 136 619 1118 1912 2792 3933 5127 6420 8103 17705 22060

1993 9 71 415 1179 1743 2742 3977 5758 7068 7515 7521 10744

1994 13 55 259 788 1468 2233 3355 4908 5931 8169 7990 15305 1995 16 54 248 654 1335 2221 3483 4713 6103 8727 7345 11258 1996 15 62 210 636 1063 1999 3344 5514 7954 8107 9334 13056 1997² 12 54 213 606 1112 1790 2851 4761 6786 6475 11176 1998² 10 47 231 579 1145 1732 2589 3930 5773 11100 14431

1999 13 55 219 604 1161 1865 2981 3991 6171 6459 18600

2000 17 77 210 559 1189 1978 2989 3797 5338 6608 10332 16570 2001 14 103 338 664 1257 2188 3145 4463 5774 8249 8931

2002 15 68 256 747 1234 2024 3190 4511 7274 7036 11904

2003 15 82 228 569 1302 1980 2975 4666 6568 8257 12826

2004 11 58 294 600 1167 1934 2657 4025 6517 7216 17500

2005 13 57 230 705 1135 1817 2948 4081 5864 8495 12308 15082

2006 15 71 288 682 1366 1991 2959 4354 5751 9631 9958

2007 19 78 253 691 1302 2128 3032 4327 6278 7837 10645 20239 2008 16 94 319 798 1393 2412 3413 5067 7070 8998 12917 12960 2009 13 83 291 724 1337 2180 3775 5267 6763 9198 8038 8100 2010 12 63 300 683 1246 2041 3076 4765 6703 8939 10386 8974 2011 15 64 255 683 1179 1933 2740 4048 5853 8043 10104 13076 2012² 13 53 214 635 1168 1706 2560 3667 5825 7489 12013 15174 2013 11 65 273 617 1211 2061 2838 3872 5018 8551 9135 14668

2014 9 53 237 629 1228 1914 2869 3944 4962 6467 8670 11397

1Estimated weights

2 Adjusted weights

Table 6.7. COD. Yearly weight increment (g) from the investigations in the Barents Sea winter 1983 - 2014.

Observations outside main areas A-S not included.

Year\Age 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10

1983-84 199 231 783 883 1196 1335 745

1984-85 148 357 582 864 1547 2222 2377

1985-86 99 206 421 620 907 485 2370

1986-87 45 111 113 383 677 1044

1987-88 93 176 262 402 255 740 403

1988-89 134 260 363 455 643 947 1866 6570

1989-90 201 422 635 831 1030 1294 1853 5866 102

1990-91 170 588 784 1058 1371 1580 1673 2969 2675

1991-92 118 423 313 548 725 1127 1570 1918 699

1992-93 51 279 560 625 830 1185 1825 1941 1095

1993-94 46 188 373 289 490 613 931 173 1101

1994-95 41 193 395 547 753 1250 1358 1195 2796

1995-96 46 156 388 409 664 1123 2031 3241 2004

1996-97 39 151 396 476 727 852 1417 1272 -1479

1997-98 35 177 366 539 620 799 1079 1012 4314

1998-99 45 172 373 582 720 1249 1402 2241 686

1999-00 64 155 340 585 817 1124 816 1347 437

2000-01 86 261 454 698 999 1167 1474 1977 2911

2001-02 54 153 409 570 767 1002 1366 2811 1262

2002-03 67 160 313 555 746 951 1476 2057 983

2003-04 43 212 372 598 632 677 1050 1851 648

2004-05 46 172 411 535 650 1014 1424 1839 1978

2005-06 58 231 452 661 856 1142 1406 1670 3767

2006-07 63 182 403 620 762 1041 1368 1924 2086

2007-08 75 241 545 702 1110 1285 2035 2743 2720

2008-09 67 197 405 539 787 1363 1854 1696 2128

2009-10 50 217 392 522 704 896 990 1436 2176

2010-11 52 192 383 496 687 699 972 1088 1340

2011-12 38 150 380 485 527 627 927 1777 1636

2012-13 52 220 403 576 893 1132 1312 1351 2726

2013-14 42 172 356 611 703 808 1106 1090 1449

Table 6.8. Survey mortality observed for cod during the winter survey in the Barents Sea in 1993-2014.

Age

Year 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9

Acoustic investigations

1993-94 0.62 0.35 -0.12 -0.01 0.53 0.54 0.78 1.08

1994-95 1.08 1.24 0.78 0.66 1.04 1.34 1.75 1.67

1995-96 2.04 1.15 0.86 0.62 1.03 1.21 1.79 1.95

1996-97 1.72 0.59 0.59 0.36 0.84 1.21 1.64 1.39

1997-98 0.94 0.01 0.03 0.20 0.39 0.32 0.49 0.86

1998-99 2.41 1.44 1.49 1.40 1.41 1.66 1.88 2.83

1999-00 0.48 0.22 -0.06 -0.39 -0.01 0.07 0.31 0.31

2000-01 0.88 0.47 0.36 0.72 1.28 1.35 1.93 2.24

2001-02 1.07 -0.08 0.21 0.52 0.50 0.79 1.37 1.25

2002-03 -1.22 -0.34 -0.50 -0.14 -0.12 0.32 0.85 0.46

2003-04 2.78 0.60 1.18 1.32 1.54 1.91 1.76 1.86

2004-05 0.28 -0.16 0.00 0.39 0.60 0.64 1.40 1.77

2005-06 0.76 0.40 0.74 0.78 0.90 0.65 1.17 1.10

2006-07 2.18 0.99 0.76 0.67 0.53 0.60 0.57 0.76

2007-08 0.25 -1.23 -1.34 -1.33 -0.83 -0.86 0.14 0.48

2008-09 0.81 -0.63 0.16 0.80 1.39 1.71 1.42 1.19

2009-10 1.69 -0.13 0.40 0.02 -0.17 -0.24 -0.10 0.40

2010-11 1.36 0.23 0.18 0.42 0.48 0.43 0.95 1.12

2011-12 1.68 -0.07 -0.11 -0.26 0.15 -0.16 0.31 0.50

2012-13 2.15 0.13 0.45 -0.30 -0.32 -0.21 0.02 0.09

2013-14 1.22 -0.69 -0.61 -0.07 0.08 0.32 0.11 0.67

Bottom trawl investigations

1993-94 0.00 0.35 -0.12 -0.05 0.36 0.53 0.95 0.89

1994-95 0.65 0.67 0.21 0.19 0.65 1.01 1.35 1.10

1995-96 2.00 1.16 0.87 0.57 0.88 1.16 1.85 1.79

1996-97 1.71 1.09 0.98 0.49 0.96 1.32 1.44 1.17

1997-98 2.01 0.97 0.27 0.56 1.00 1.09 1.19 1.74

1998-99 1.96 1.11 0.83 1.14 1.00 1.38 1.25 1.97

1999-00 0.67 0.37 0.47 0.47 0.77 1.14 1.18 1.45

2000-01 0.52 0.26 0.25 0.46 1.04 1.11 1.36 1.61

2001-02 0.39 -0.14 0.35 0.51 0.67 0.93 1.31 1.30

2002-03 -0.81 0.16 -0.38 0.39 0.49 0.84 1.13 0.88

2003-04 2.54 0.03 0.78 0.82 0.71 0.90 0.89 1.06

2004-05 0.38 -0.05 0.21 0.56 0.83 1.06 1.80 1.93

2005-06 1.05 0.64 0.79 0.77 0.81 0.89 1.15 1.17

2006-07 0.78 -0.24 0.33 0.57 0.66 0.89 0.75 1.00

2007-08 1.66 0.73 0.10 -0.07 0.29 0.13 0.71 0.88

2008-09 0.59 -0.25 -0.14 0.54 0.44 0.88 0.65 0.59

2009-10 1.30 0.08 0.10 0.31 0.32 0.38 0.50 0.66

2010-11 1.52 0.17 -0.41 -0.13 0.14 0.39 0.87 1.12

2011-12 0.63 0.82 0.25 0.19 0.34 0.12 0.59 0.75

2012-13 2.12 1.50 -0.12 0.05 0.23 0.35 0.45 0.67

2013-14 0.96 -0.06 -0.13 0.50 0.30 0.25 0.33 0.87

6.4 Stomach sampling

Since 1984, cod stomachs have been sampled regularly during the winter survey. The sampling strategy has generally been the same as that for sampling otoliths. Stomach have been frozen onboard and analysed in the laboratory, except for the period 1994-2000, when some of the stomachs were analysed onboard and only the main prey categories were identified. For details about the sampling methodology and the Norwegian-Russian cooperation on diet investigations in the Barents Sea, see Mehl and Yaragina (1992) and Dolgov et al. (2007).

The number of stations and stomachs sampled as well as the proportion of empty stomachs and the mean stomach fullness index (SFI, see below) for each of 4 size groups ( ” 19 cm, 20- 34 cm, 35-49 cm, • 50 cm) is given in Table 6.9. Table 6.10 - 6.13 show the mean diet composition by prey species/groups by year for each size group. Note that in the years 1994- 2000, blue whiting, long rough dab and Norway pout were included in the category ‘other fish’ when stomachs were analysed onboard.

The stomach fullness index is calculated as SFI

=100*ȈWS

/W

, where WS

is the weight (g) of the stomach of fish i, and W

is the weight (g) of fish i. For 1987 SFI has not been calculated, because very few fish were weighed that year due to technical problems. The distribution on prey groups has been adjusted by distributing the unidentified component of the diet proportionally among the various components, taking into account the level of identification.

The geographical distribution of stomach fullness and prey composition divided into three prey categories (capelin, other fish, other food) by length group and year is shown in Figures 6.5-6.6. The proportion of empty stomachs is largest for the smallest fish (Table 6.9), a pattern seen for all years. Capelin is the dominating prey for cod ш 20cm (Tables 6.11-6.13), while krill dominates for the smallest cod (Table 6.10). However, in many years capelin is also an important prey for the smallest cod. The diet composition in 2013-2014 was generally similar to that in the period 2008-2012. The stomach fullness index SFI was generally lower than in the period 2008-2012. In particular, the SFI for the largest fish (>= 50cm) in 2014 was the lowest since 1998, and the proportion of capelin in the diet of this size group in 2014 was the lowest since 2009. Reasons for this could be both that the 2014 survey also covered the area west of Svalbard, where capelin is scarce, and also that the proportion of the fish >=

50cm which is mature is higher than in previous years. Mature fish probably feeds less intensively than immature fish at this time of the year.

The highest stomach fullness is found in the south-eastern part of the survey area and along

the coast of Norway and Russia. However, there are also in most years some stations with

high stomach fullness close to the northern limit of the survey area. In the western part of the

Barents Sea and west of Svalbard the SFI is generally low.